Question: Simplify the following expression and state the condition under which the simplification is valid. $x = \dfrac{k^2 - 9}{k - 3}$
First factor the polynomial in the numerator. The numerator is in the form ${a^2} - {b^2}$ , which is a difference of two squares so we can factor it as $({a} + {b})({a} - {b})$ $ a = k$ $ b = \sqrt{9} = -3$ So we can rewrite the expression as: $x = \dfrac{({k} {-3})({k} + {3})} {k - 3} $ We can divide the numerator and denominator by $(k - 3)$ on condition that $k \neq 3$ Therefore $x = k + 3; k \neq 3$